JP2009041131A - Method for producing coated white paperboard and coated white paperboard - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing a coated white paperboard having a pigment-coated layer by which dust and black spots of a base paper are concealed to make them indistinctive, and white color unevenness is reduced, and to provide the coated white paperboard. <P>SOLUTION: The method for producing the coated white paperboard by forming a pigment coated layer containing a pigment and an adhesive as main components on one or both surfaces of the base paper obtained by combining at least two or more layers, includes coating the pigment-coating layer, the opacity of which is 50% or more by a curtain coating method. The coated white paperboard is produced by the production method. The base paper preferably has a difference of whiteness of 12% or more between the surface layer at the surface to be coated and the layer just below the surface layer. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a coated white board having a pigment coating layer on a base paper mixed with used paper, and a method for producing a coated white board which conceals dust and black spots derived from used paper, suppresses white unevenness and improves the white paper surface feeling. And its coated white paperboard.

  White paperboard is usually classified into white balls and manila balls, and manila balls are further classified into high-grade white paperboard and special white paperboard. Furthermore, white balls and manila balls have a coating type and a non-coating type. White paperboard is usually a cardboard having a multilayer structure of 2 to 9 layers, and used paper pulp is often used from the viewpoint of environmental aspects and cost reduction of packaging materials. For example, in white balls, bleached pulp or deinked and bleached waste paper pulp having high whiteness is used for the surface layer, and waste paper pulp having low whiteness is used for the middle layer and the back layer. The ratio of waste paper pulp is increasing year by year, and almost 100% of low-grade white paperboard is added. Under such circumstances, the problems of the base paper accompanying the increase in the ratio of used paper include the appearance of white unevenness and the increase of defects such as dust and black spots. Defects such as dust have been greatly improved by advances in deinking technology and dust removal equipment, but have not yet been completely removed. Since the stronger the current deinking and dust removal treatment, the worse the yield and the economical disadvantage, no deinking and dust removal processing is performed above a certain level. Under these circumstances, white paperboard is often used as a container for foodstuffs, pharmaceuticals, cosmetics, etc., especially for coated white paperboard, there is an increasing demand for improvements in appearance and printability from the viewpoint of visualization. Yes.

  From the viewpoint of environmental issues, the use of waste paper will continue to increase in the future, so it is possible to apply it to the surface as a technology that effectively makes dust less noticeable and improves whiteness and printability while using paper with a lot of waste paper. A method of increasing the coating amount to be applied or blending a large amount of an organic pigment such as titanium dioxide or plastic pigment having high concealability is disclosed. (See Patent Documents 1 and 2) However, these pigments are expensive, and the physical properties of the paint are greatly changed, so that it is difficult to use them in large quantities. In addition, as a method for making the white unevenness of the base paper inconspicuous, a proposal has been made that defines the difference in whiteness between the surface layer and the lower layer in the multilayer papermaking. (See Patent Document 3)

JP-A-6-166991 JP 2003-306882 A JP 2005-298998 A

  Waste paper pulp is used for coated base paper after deinking ink and removing dust, etc., but it is difficult to completely remove fibers and dust with a small amount of ink attached. It is derived from mechanical pulp, and even if pulp bleaching is performed, there is a limit in improving the whiteness. In white paperboard, the ratio of used paper pulp is high, conditions may not be constant depending on the type and state of used paper, dust and black spots are likely to appear on the surface of the base paper, and white base paper unevenness tends to be noticeable. When providing a pigment coating layer on such a base paper, the blade coating method is a flattening coating, and the smoothness of the coating surface is high, but the pigment coating layer is uneven along the irregularities of the base paper. As a result, white unevenness is conspicuous. Coating defects such as streaks and scratches are also likely to occur. The roll coating method tends to generate a pattern specific to the roll, and the air knife coating method tends to generate a pattern specific to the air knife. Accordingly, an object of the present invention is to provide a method and a coated white paperboard for producing a coated white paperboard in which dust and black spots on the base paper are almost concealed so as to be inconspicuous and white unevenness is suppressed.

As a result of earnest research on the relationship between the base paper and the white unevenness after coating, dust, black spots, white unevenness is conspicuous with a lot of waste paper pulp, and contour coating is applied to white paperboard with a lot of dust. It was found that a pigment coating layer is provided using a curtain coater characterized by the following, and that the coating layer has a specific opacity, thereby concealing dust and black spots and suppressing white unevenness. That is, in a method for producing a coated white paperboard in which a pigment coating layer mainly composed of a pigment and an adhesive is provided on one or both sides of a base paper that is made of at least two layers, the pigment coating layer is a curtain coating method. The method for producing a coated white board and the coated white board, wherein the opacity of the pigment coating layer is 50% or more. Moreover, it is preferable if the white paper has a difference in whiteness between the surface layer of the surface on which the base paper is coated and the layer immediately below it is greater than 12%. Moreover, it is preferable if the coating amount per one side of the pigment coating layer is 1 to 25 g / m ² . Furthermore, it is more preferable if the B-type viscosity at the time of coating of the pigment coating solution to be formed to form the pigment coating layer is 30 to 2000 mPa · s and the surface tension is 40 mN / m or less.

Conventionally, the base paper weight of white paperboard is 150 g / m ² or more, and it is not easy to make a base paper with one paper machine. Usually, several paper machines are lined up and the base papers are combined. At this time, when a raw material having a high waste paper pulp content is used, unevenness in papermaking and unevenness in the base paper is likely to occur, and white unevenness is also generated at the same time. In particular, by making these base papers together, white unevenness is further promoted and appears remarkably. For example, in white paperboard using waste paper pulp not deinked in the middle layer, the surface area of the surface is about 20-60 g / m ² , and the concealability is low, and the base paper texture of each layer obtained with a normal paperboard machine is Due to the machine structure such as a circular net, a long net with a short distance, and a combination of short nets, it is often inferior to a paper-based long net machine, and as a result, the surface layer has a low pulp content (high transparency) and The difference in the part with a large amount of pulp (low transparency) is relatively large, and when this layer is combined with the following layers, the surface part of the surface layer is the part with the small amount of pulp in the surface layer (high transparency) If the whiteness difference between the surface layers of the surface layer and the surface layer is large, the portion where the surface of the surface layer is reflected is white unevenness. This can be said to be the same as the surface layer and the lower layer also about the white paperboard base paper which is multi-layered with the back surface and the lower layer.

  Such white unevenness of the base paper is a problem in practical use, and becomes apparent particularly when the difference in whiteness between the surface layer and the immediately lower layer is larger than 12%. The whiteness unevenness can be improved by a method in which the whiteness of the immediate lower layer is increased in advance to approximate the whiteness of the surface layer, or the whiteness of the surface layer is decreased to approximate the whiteness of the immediate lower layer. However, it is difficult to implement stably because of constraints such as cost, selection of pulp to be used, and securing of amount. For this reason, if the difference in whiteness between the surface layer and the layer immediately below it is large, even if a pigment coating layer is provided on the surface layer, white unevenness will not be improved. It must be used. However, since such pigments are expensive, their use in large quantities is economically difficult. Therefore, from the viewpoint of concealment of the base paper, a pigment coating layer is provided on the white paperboard base paper, which has a particularly high ratio of used paper, using a curtain coater, and the opacity of the pigment coating layer is 50%. It was found that the above is effective. Here, the curtain coating method is an effective coating method, because the coating method is a pre-metering type coating device and there is no scraping off of the coating solution during coating. Forms a very uniform so-called contour coating layer along the surface shape of the web, and even if there are some irregularities on the base paper, the coating layer is uniform, so the occurrence of coating unevenness is suppressed. I think. Furthermore, by setting the opacity of the pigment coating layer to 50% or more, it is possible to improve the concealability and suppress white unevenness.

  According to the present invention, a pigment coating layer is provided by curtain coating on a base paper blended with waste paper, and the pigment coating layer has a specific opacity, thereby concealing dust and black spots derived from waste paper and suppressing white unevenness. Coated white paperboard can be obtained.

The pulp composition of the base paper used in the present invention is not particularly limited. For example, one or two or more of bleached or unbleached chemical pulp, mechanical pulp, deinked or undeinked pulp waste paper pulp, and the like are used as appropriate. In addition, a sizing agent, a paper strength agent, a chemical stabilizer, a filtering agent, a filler, a dye, and the like can be appropriately added to the base paper as necessary. The base weight of the base paper is usually about 150 to 650 g / m ² .

  The base paper usually contains a filler, and the filler is not particularly limited. For example, clay, calcined clay, diatomaceous earth, talc, kaolin, calcined kaolin, deramikaolin, heavy calcium carbonate, light Calcium carbonate, magnesium carbonate, barium carbonate, titanium dioxide, zinc oxide, silicon oxide, amorphous silica, aluminum hydroxide, calcium hydroxide, magnesium hydroxide, zinc hydroxide and other inorganic fillers, urea-formalin resin, polystyrene resin Organic fillers such as phenol resin and fine hollow particles, and fillers contained in waste paper or broke are used alone or in appropriate combination of two or more. The blending ratio of the filler is preferably 5 to 20 parts by mass with respect to 100 parts by mass of the pulp. In addition, since the interlayer intensity | strength of paper will become low when the mixture ratio of a filler increases, it is necessary to aim at harmony with paper quality.

  In addition, as a paper machine for obtaining the base paper, a paper machine such as a long net paper machine, a short net paper machine, a circular net paper machine, an on-top former, and a gap former can be used. Make a base paper by combining.

  For the formation of the pigment coating layer, a pigment coating liquid mainly composed of a pigment and an adhesive is applied, and the pigment contained in the coating liquid does not need to be special, but the conventional publicly known publicly used For example, clay, kaolin, aluminum hydroxide, calcium carbonate, titanium dioxide, barium sulfate, zinc oxide, satin white, calcium sulfate, talc, plastic pigment, organic hollow fine particles, etc. Pigment. Examples of the adhesive used include water-soluble polymers such as starch, casein, polyvinyl alcohol, methyl cellulose, carboxymethyl cellulose, hydroxymethyl cellulose, and polyacrylic acid, styrene-butadiene copolymer latex, and styrene-acrylic acid. One type or two or more types of natural or synthetic adhesives such as copolymer latex can be appropriately used.

  The blending ratio of the pigment and the adhesive in the coating liquid is adjusted within a range in which a desired pigment coating layer can be obtained. Usually, the adhesive is selected in the range of 5 to 50 parts by mass, more preferably 5 to 30 parts by mass with respect to 100 parts by mass of the pigment. In a coating composition, various adjuvants, such as an antifoamer, a coloring agent, a mold release agent, and a flow modifier, can be mix | blended as needed.

  The coating property when the pigment coating solution for forming the pigment coating layer in the present invention is applied with a curtain coater is that coating defects occur due to cracking of the curtain film during the flow of the coating solution. From the viewpoint of prevention, it is preferable that the B-type viscosity is 30 to 2000 mPa · s and the surface tension is 40 mN / m or less.

  In order to sufficiently conceal the surface of the base paper where dust, black spots and white unevenness derived from used paper are concealed and to suppress white unevenness, a pigment coating layer is formed by a curtain coating method using a pigment coating solution, and the coating layer It is essential that the opacity of the glass be 50% or more. Here, the opacity of the pigment coating layer is applied to a transparent PET film (thickness 75 μm, opacity 5% or less), and the opacity of the coating film at that time is measured according to JIS P-8149: 2000. Can be obtained. Incidentally, when the coating amount is less than 50% of the opacity of the pigment coating layer, the effect on white unevenness is not recognized, and even if it is 50% or more, the effect can be obtained by a coating method other than curtain coating. Absent.

  Here, as a coating layer other than the pigment coating layer by curtain coating, an overcoating layer or an undercoating layer may be provided, but in particular, if an undercoating coating layer is provided before curtain coating, This is preferable because it has the effect of further highlighting the contour coating, which is a feature of the above. For this undercoat layer, a coating apparatus used in the general coated paper manufacturing field can be used. For example, a blade coater, an air knife coater, a plain rod coater, a roll coater, a reverse roll coater, a bar coater, a die slot coater, A coating apparatus such as a gravure coater, a Chanplex coater, a 2 roll size press coater, a gate roll size press coater can be used on-machine or off-machine.

The coating amount of the coated liquid, 1 to 25 g / ^{m 2} on one surface per dry weight, more preferably from 3 to 15 g / ^{m 2.} When two or more pigment coating layers are provided on one side of the base paper, for example, the total dry coating amount of the curtain coater coating layer and the coating layer by another coating method is 1 to 25 g / side. Within the range of m ² , the coating amount of each layer may be distributed in consideration of the desired suppression of white unevenness. Incidentally, if it is less than 1 g / m ² , the coating stability and the base paper coverage are insufficient, and if it exceeds 25 g / m ² , the coating layer may be cracked.

  The coated white paper board obtained in this way is usually passed through a calendar and subjected to pressure smoothing, and then finished as a wound product. The calendar device in this case is not particularly limited, and various calendars composed of a metal roll and an elastic roll such as a super calendar, a gloss calendar, and a soft compact calendar can be used as a gloss or mat calendar. It is arbitrarily selected and used in machine specifications.

  EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples. In the examples and comparative examples, “parts” and “%” indicate “parts by mass” and “% by mass” in terms of solid content, respectively, unless otherwise specified.

Example 1
(Raw paper)
Using pulp blended at a ratio of LBKP 70%, NBKP 20%, and deinked waste paper 10%, it was blended at a ratio of whiteness 79.7%, surface area of 40g / m ² , LBKP 40%, deinked waste paper 60% Using a pulp, whiteness of 66.7%, surface area of 40 g / m ² , paper weight of 40 g / m ² , middle layer of non-deinked magazine paper of 150 g / m ² Using pulp blended at a ratio of 25% used magazine paper and 25% used corrugated cardboard, each 50 g / m ² back layer is made, combined, pressed, and dried to apply 280 g / m ² A white paperboard base paper was obtained.

(Preparation of pigment coating solution 1)
As a pigment, No. 1 kaolin (trade name: UW-90, manufactured by BASF) 50%, light calcium carbonate (trade name: TP-123CS, manufactured by Okutama Kogyo Co., Ltd.) 50% is used. Sodium acrylate 0.2% was added, and a pigment slurry having a solid content of 68% was prepared using a Coreless disperser. And, with respect to 100 parts of pigment in the pigment slurry, 3 parts of oxidized starch (trade name: Ace A, manufactured by Oji Cornstarch), styrene-butadiene copolymer latex (trade name: L-) having a glass transition temperature of 8 ° C. 1825 (manufactured by Asahi Kasei Co., Ltd.) was added to each (in terms of solid content), and water was further added to prepare pigment coating solution 1 having a solid content concentration of 60% and a B-type viscosity of 900 mPa · s.

(Creation of coated white paperboard)
After adding 0.2% of a surfactant (trade name: Orphine WE-003, manufactured by Nissin Chemical Co., Ltd.) to the pigment coating solution 1 on the surface layer of the base paper and diluting to a solid content concentration of 30%, the curtain Using a coater, after coating and drying so that the dry weight per side is 7 g / m ² , the paper roll is passed through a soft calender with a surface temperature of 150 ° C. and 2 nips to obtain a coated white paperboard. It was. At this time, the B-type viscosity of the pigment coating solution in curtain coating was 60 mPa · s, and the surface tension was 30 mN / m.

Example 2
Performed in the same manner as in Example 1 except that a pulp blended in a ratio of 25% LBKP and 75% deinked waste paper was used to obtain a surface layer having a whiteness of 61.9% and a rice basis weight of 40 g / m ^2. A coated white paperboard m ² was obtained.

To the above base paper, 0.2% of a surfactant (trade name: Orphine WE-003, supra) is added to the pigment coating solution 1 of Example 1, diluted to a solid content concentration of 40%, and then a curtain coater. The coated white paperboard was obtained in the same manner as in Example 1 except that coating and drying were performed so that the dry weight per side was 10 g / m ² . The B-type viscosity of the pigment coating liquid at this time was 200 mPa · s, and the surface tension was 30 mN / m.

Example 3
280 g / m of rice tsubo in the same manner as in Example 1 except that a pulp blended at a ratio of 10% LBKP and 90% deinked waste paper was used to make the outer layer of whiteness 56.1% and rice tsubo 40 g / m ^{2. 2} coated white paperboard base paper was obtained.

To the above base paper, 0.2% of a surfactant (trade name: Orphin WE-003, supra) is added to the pigment coating solution 1 of Example 1, diluted to a solid content concentration of 55%, and then a curtain coater. A coated white paperboard was obtained in the same manner as in Example 1 except that the dry weight was 14 g / m ² per side and the coating was dried. The B-type viscosity of the pigment coating solution at this time was 400 mPa · s, and the surface tension was 30 mN / m.

Example 4
(Preparation of pigment coating solution 2)
As pigments, No. 1 kaolin (trade name: UW-90, supra) 50%, light calcium carbonate (trade name: TP-123CS, supra) 30%, titanium dioxide (trade name: KA100, manufactured by Titanium Industry Co., Ltd.) 20 As a dispersant, 0.2% sodium polyacrylate was added to the pigment, and a pigment slurry having a solid content concentration of 68% was prepared using a Coreless disperser. And with respect to 100 parts of pigments in the pigment slurry, 3 parts of phosphate esterified starch (trade name: PN500, manufactured by Sanwa Starch Co., Ltd.) and a styrene-butadiene copolymer latex (trade name) having a glass transition temperature of 8 ° C. : L-1825, supra) 20 parts (in terms of each solid content) were added, and water was further added to prepare pigment coating solution 2 having a solid content concentration of 60% and a B-type viscosity of 1000 mPa · s.

After adding 0.2% of a surfactant (trade name: Olfin WE-003, supra) to the pigment coating liquid 2 and diluting to a solid concentration of 30%, using a curtain coater, the dry weight per side After coating and drying the base paper of Example 1 so as to be 8 g / m ² , the paper roll was passed through a soft calender having a metal roll surface temperature of 150 ° C. and 2 nips to obtain a coated white paperboard. At this time, the B-type viscosity of the pigment coating solution in curtain coating was 60 mPa · s, and the surface tension was 30 mN / m.

Example 5
(Preparation of pigment coating solution 3)
As pigments, No1 kaolin (trade name: UW-90, supra) 20%, light calcium carbonate (trade name: TP-123CS, supra) 30%, titanium dioxide (trade name: KA100, supra) 50% Used, as a dispersant, 0.2% of sodium polyacrylate was added to the pigment, and a pigment slurry having a solid content concentration of 60% was prepared using a coreless disperser. And, with respect to 100 parts of pigment in the pigment slurry, 3 parts of oxidized starch (trade name: Ace A, supra) and styrene-butadiene copolymer latex (trade name: L-1825, glass transition temperature of 8 ° C.) As described above, 20 parts (in terms of each solid content) were added, and water was further added to prepare a pigment coating solution 3 having a solid content concentration of 50% and a B-type viscosity of 1500 mPa · s.

After adding 0.2% of a surfactant (trade name: Olphine WE-003, supra) to the pigment coating solution 3 and diluting to a solid content concentration of 20%, using a curtain coater, the dry weight per side After coating and drying the base paper of Example 1 so as to be ² g / m ² , the paper roll was passed through a soft calender having a metal roll surface temperature of 150 ° C. and 2 nips to obtain a coated white paperboard. At this time, the B-type viscosity of the pigment coating solution in curtain coating was 150 mPa · s, and the surface tension was 25 mN / m.

Comparative Example 1
Except for diluting the pigment coating solution 1 to a solid content of 40% on the base paper of Example 1 and then coating and drying it using an air knife coater so that the dry weight per side is 7 g / m ^2. The coated white board was obtained in the same manner as in Example 1. The B-type viscosity of the pigment coating solution at this time was 200 mPa · s.

Comparative Example 2
Example 1 except that the pigment coating liquid 1 was applied to the base paper of Example 1 with a solid content concentration of 60% and dried using a rod coater so that the dry mass per side was 7 g / m ^2. In the same manner as above, coated white paperboard was obtained.

Comparative Example 3
Example 1 except that the pigment coating liquid 1 was applied to the base paper of Example 1 with a solid content concentration of 60% and dried using a blade coater so that the dry weight per side was 7 g / m ^2. In the same manner as above, coated white paperboard was obtained.

Comparative Example 4
A coated white paperboard was obtained in the same manner as in Comparative Example 1 except that it was replaced with the pigment coating solution 2 in Comparative Example 1 and coated and dried so that the dry weight per side was 10 g / m ² .

The B-type viscosity and surface tension of the pigment coating solution used above were measured by the following evaluation methods.
(B type viscosity)
It was measured under the condition of 60 rpm with a B-type viscometer (model: BM, manufactured by Tokyo Keiki Co., Ltd.) and used as the viscosity of the pigment coating solution.

(surface tension)
The surface tension of the pigment coating solution was measured by a Wilhelmy plate type surface tension meter (model: CBVP-Z, manufactured by Kyowa Interface Science Co., Ltd.).

(Evaluation of white unevenness and concealment)
The coated base paper used in each Example and Comparative Example and the obtained coated white paperboard were subjected to sensory evaluation by visual observation from above. The results are shown in Table 1.

[Evaluation criteria for white unevenness]
A: Generation of white unevenness is not recognized.
○: Occurrence of mild white unevenness is observed.
(Triangle | delta): Generation | occurrence | production of clear white nonuniformity is recognized and is a level which is a problem practically.
X: Extremely white unevenness was observed and was not suitable for practical use.

[Evaluation criteria for concealment of dust and sunspots]
A: Not noticeable at all.
○: Mild dust and sunspots are observed.
Δ: Clear dust and sunspots are recognized and practically problematic.
X: Extremely dusty / spots are recognized and not suitable for practical use.

  As can be seen in Examples 1 to 5 according to the present invention in Table 1, by performing curtain coating and providing a pigment coating layer having an opacity of 50% or more, the occurrence of white unevenness is suppressed, and concealment is achieved. On the other hand, good results are obtained, while it is clear that the concealability and whiteness unevenness are not improved by the other coating methods seen in Comparative Examples 1 to 4.

Claims (5)

  In a method for producing a coated white paper board in which a pigment coating layer mainly composed of a pigment and an adhesive is provided on one side or both sides of a base paper that is made of at least two layers, the pigment coating layer is applied by a curtain coating method. A method for producing a coated white paperboard, wherein the opacity of the pigment coating layer is 50% or more.   The method for producing a coated white board according to claim 1, wherein the white paper has a difference in whiteness between the surface layer of the surface on which the base paper is coated and the immediately lower layer of the base paper is greater than 12%. The manufacturing method of the coated white paperboard of Claim 1 or 2 whose dry coating amount per one side of the said pigment coating layer is 1-25 g / m < ² >.   The B-type viscosity at the time of coating of the pigment coating solution to be coated for forming the pigment coating layer is 30 to 2000 mPa · s and the surface tension is 40 mN / m or less. A method for producing a coated white board according to one item.   Coated white paperboard manufactured with the manufacturing method as described in any one of Claims 1-4.